1. Field of the Invention
The present invention relates to an innovative chain tightener.
2. State of the Prior Art
In chain transmissions between two sprocket wheels there is always one branch under tension and a slack branch. It is often important to hold the oscillations of the slack branch under control to avoid excessive flapping and noise of the chain and resulting premature wear paired with reduced efficiency. To achieve this, slack branch tightening systems consisting either of fixed runners whose position is adjusted manually according to need or by automatic tighteners consisting of a runner thrust against the slack chain branch are normally used.
Under particular operating conditions the tension of the two chain branches can be reversed so that the branch which was slack first becomes the tight branch and vice versa.
A special case of chain transmission subject to such pull reversal is the primary transmission between motor and gearbox used on some motor vehicles and automobiles.
When there is a reversal of load on the transmission, for example during an abrupt deceleration, the tight branch becomes slack while the slack branch becomes tight. In such a situation, if the tightener runner backs under the thrust of the chain, an uncontrolled slack branch is formed where previously there was a tight branch. Vice versa, if the tightener runner does not back, both chain branches remain reasonably under control but the runner and the tightener have to withstand a strong thrust which could lead to accelerated wear of the runner and sagging because of fatigue of the antireturn mechanism which is usually provided for recovery of play caused by progressive lengthening of the chain.
Use of two retractable tighteners, one per branch, driven by a simple spring, does not solve the problem because even if the runners tend to follow the two branches of the chain the springs tend to trigger harmful oscillations.
The general purpose of the present invention is to remedy the above mentioned shortcomings by making available a tightener acting in a satisfactory manner on the slack branch of the chain whichever it might be while compensating for the play and avoiding harmful stress.